Electronic ignition system



Dec. 31, 1968 H. F. slLvERMAN 3,413,989

ELECTRONIC IGNITION SYSTEM Filed May 17, 1967 wwwa@ X III MON fom III# (-HI- @HIP S m M m T M N N w V T N l T I S A E m V. w on A H Y B Y .nv ,m,\ N\ Nm N mmow Em I \Nm, T N NN MI NN I mi ON N N L INI @m QW, N INEI @NIL o I ol .,ysewf@ Jv S s o o o Jv 31, 1968 H. F. slLvERMAN 3,418,989

A ELECTRONIC IGNITION SYSTEM med may 17, 1967 sheet 2 CYL 2 CYL 3 F Q 5 |NVENTOR HARVEY F. S|LVERMAN ATTORNEYS States 3,418,989 ELECTRQNIC IGNlTlGN SYSTEM Harvey F. Silverman, 101 N. Broadway, East Providence, RJ. 02916 Filed May 17, 1967, Ser. No. 639,116 2 Claims. (Cl. 12S-148) AESTRACT F THE DKSCLQSURE Background 0f the invention This invention relates to ignition systems which until recently have been the same that was introduced just after the changeover from the magneto about 1910. It has been recognized -by many that the breaker points in the conventional ignition systems are the weak link of the system, for it is these points that switch large current. A capacitor, of course, is utilized to lengthen the life of the points but regardless of this the points will usually wear from arcing, oxidation and other related phenomena. The other critical element in conventional ignition systems is the distributor. The usual distributor has no contact between the rotor and the poles of the distributor cap. This means, of course, that a fair amount of energy is dissipated in crossing the gap and while in dry air this energy loss is not significant,

it does take on significant aspect when operating in damp conditions since it takes much more energy to ionize the air gap and thus engine performance in damp conditions may be poor due to misfirings.

A iirst approach to solving this problem was to utilize a transistor as a switch for the primary current of the coil. With this type of system there are still some aspects that have not been corrected since we have continued to use breaker points that can still wear from mechanical deterioration and have a distributor that can still cause problems as noted above and have added a new situation where the high energy losses of the primary of the coil make the system very inetiicient. Some of the power losses that occur in the conventional transistor circuits are cured to some degree by the capacitor discharge systems that have become common and which, for example, are discussed in U.S. Patent 3,184,653.

The present invention is totally electronic and has a minimum number of moving parts, namely, one moving part, which is utilized both for timing and distribution. Broadly the output from the distribution system is taken and raised to a voltage level that is suiiicient to cause sparking of a conventional spark plug. One method of providing electronic distribution is suggested in the Gilbert Patent 2,811,672 where in eiiect a sensing device is used for each cylinder. The system used by Gilbert, however, does not include provision for timing except by varying a bias source which changes the trigger level of the gas discharge tubes. It is preferable to create a timing signal in connection with the distribution, and this suggests the use of a shaft encoder to create shaft position and timing signals together with a gate decoder system to separate the different cases to lire the individual cylinders.

3,418,939 Patented Dec. 31, 1968 Silrnim'ary of the invention A shaft position encoder is utilized to create both shaft position signals and timing signals. The encoder has one strobe channel for producing a timing output for each cylinder and n position encoding channels where 2n is greater than or equal to the number of cylinders. For an eight-cylinder engine, three positional indication lines would be necessary to give eight possible combinations, and thus by utilizing a timing signal there must be utilized for an eight-cylinder engine four sensors. The sensor outputs `are fed to a logic network which may consist of an amplifier and an inverter so that all combinations may be gated With a timing line in order to get the distributor outputs desired. Thus basically the outputs of the pulse amplifiers and inverters are fed to NAND gates, which in turn feed a suitable spark discharge producing device which is illustrated as being on the capacitive discharge type.

Brie]l description of the drawings FIG. 1 is a schematic diagram partially in block form of an electronic ignition system according to the present invention;

FIG. 2 is a schematic diagram of a circuit which may be employed as the NAND gate circuit;

FIG. 3 is a schematic diagram of a suitable capacitor discharge trigger circuit;

FIG. 4 is a sectional view of an optical shaft encoder `for an eight-cylinder engine;

FIG. 5 is a plan view of the encoder disc utilized for an eight-cylinder engine; and

FIG. 6 is a wave form diagram of the inputs to the NAND gates.

Description of the preferred embodiment With reference to FIG. 1 0f the drawings, there is shown therein an optical shaft encoder generally designated 10 which consists of a light source portion 11, a number of tracks which are generally designated 12 and a number of light sensors generally designated 13. Preferably for the light source 11 a number of low voltage long-life bulbs connected in parallel are shown and as shown more particularly in FIG. 4 these light sources may be conveniently mounted in a housing 15 that is mounted generally above the main housing of the encoder which housing has been designated with the numeral 16. A breaker disc 20 is mounted on a shaft 21 which is supported in a pair of bearings 22, 23. Intermediate in the encoder housing 16 is a circular plate 2S into which the sensors 13 are mounted. Each of these `sensors is provided with a masked down receiving area that is provided by the apertures such as 27 that lead to the main sensor bodies as at 28. This serves two purposes, one in giving a high signal to noise ratio and eiiectively isolating the desired information from any stray shadows that might be present within the device. Preferably the breaker disc 20 is scribed on one side which is closest to the input apertures 27 to the sensors. As shown in FIG. 4 the masking is provided by embedding the blacked out areas into the clear disc 20 on the underside as for example at 29 and to further prevent any stray light from causing reiiections and shadows, the entire area within the encoder body 16 is dulled and preferably painted or otherwise coated with a dull black paint or the equivalent. The only area which is made reliective is the area within the housing 15 which is preferably made white or other highly reiiective surface utilized so that as much light as possible will be emitted from this light source area. The light sensors that are utilized for the elements generally designated 13 that may take a variety of forms. For example, they may be photovoltaic diodes or they may lbe photo-transistors or equivalent devices which will produce a signal output when exposed to light.

Assuming that a standard photovoltaic diode is utilized the weak to 25 micro ampere output of this type of sensor must be amplified with a great degree of stability. For example, in todays technology in order to achieve a high current gain a Darlington circuit is ideally suited and lends itself to being a direct coupled circuit when made in two stages or more.

In utilizing this arrangement, the diagram of FIG. 1 has eliminated any reference to a standard amplifier and effectively shows the output of the sensors being directly coupled into inverters in distribution lines which inverters are designated as 30, 31 and 32. These inverters are single input NAND gates. Thus in the three lines we have true and false logic which may then be distributed to a four input gate such as is illustrated in FIG. 2 of the drawings and which are represented in the block diagram by the reference numerals 33 to 4t? inclusive. The NAND function is achieved at the collector of the transistor 4Z of the gate. If the level of 3.9 volts is taken as true or a logical 1 and the zero volt level is taken as false or a logical zero, the performance of the gate may be seen.

Should all the input levels to the gate be 3.9 volts or all logical 1, then a small current will iiow through resistor 43, Zener diodes 44, 455 and resistor 46 to ground. By a voltage division the base voltage of the transistor is thus about l volt, which means that the transistor 42 is forward biased and conducts. The voltage at the collector is approximately zero volts and a logical zero. In this manner the first condition for the NAND gate is met. Now when any of the input diodes 48, 49, 50 and 51 has a zero volt level placed on it, current flows from the negative supply through resistor 43 and out to the apparent ground through the forward biased input diode. The level at the `cathode side of the input diode is thus about zero volts. This level necessarily appears at the base of the transistor, and therefore, the transistor is biased into a non-conducting state. The voltage at the collector of the transistor 42 is thus 3.9 volts or a logical l. In this manner the second condition for the NAND gate is met.

To obtain an efiicient operation, an electronic advance is made a part of the system by placing a delay means 55 in the strobe line. This delay means may consist of multi-vibrators as for example a pair of one-shot multivibrators, the retard time being set in the first of the two one-shot multi-vibrators. The second multi-vibrator would be used as the strobe pulse line. Its pulse time would be set to that of the strobe itself while the delay time of the first multi-vibrator would be varied by sensors of both engine speed and engine load. With this method a very precise and consistent advance can be applied to the engine.

A casual inspection of FIG. 6 of the drawings with comparison of FIG. l wherein the inputs to the gate are disclosed will readily reveal the functioning of the apparatus of this invention without the need for setting up a truth table. Taking cylinder No. 1 which is designated by the Roman numeral I, for example, it will be noted that the input to the gate 33 is the inverted output of channels 20, 21 and 22. According to FIG. 6 for cylinder No. 1, all of the inputs will be the minus Voltage level which We described above as being 3.9 volts to be consistent with the circuit diagram of FIG. 2, and then it will be seen that all these input levels to the gate will be at 3.9 volts or all a logical one whereupon the transistor 42 of FIG. 2 will conduct and give us an output. Further veriiication of this situation can be had by referring to FIG. 5 where the encoder disc shows channels 21 which is the inner channel as being clear, the channel 22 which is the intermediate channel as being clear and channel 2 which is the outer channel as also being clear. Accordingly, in order to have every input at the same level, it is necessary with the strobe that all be inverted which is the condition illustrated in FIG. 6. Similar analogy may be carried forward for any of the other cylinders, as for example, if we assumed the situation at cylinder VI, we tind that the input there consists of channel 2 inverted channel 21 and channel 22. Again we find that all of these voltages are eectively 3.9 volts again referring to the condition set forth in FIG. 2 and again the proper conditions being met a pulse will be fed on to the trigger and spark discharge for cylinder 6. It will be particularly apparent by examining the diagram of FIG. 6 that the actual position of the cam shaft is detected at all times. There is also no chance for a stray pulse to cause a catastrophe since the gates in the decoder section are always set up for the correct cylinder. This means that the decoding is wired as shown in FIG. 1 so that it is a failsafe system and very little logic is necessary since all of the logic is made up of gate circuits. A further advantage which accrues with this arrangement is in the length of the pulse that may be generated by each of the tracks wherein the strobe pulse is in effect located intermediate the track generated pulses and may be advanced and retarded to any degree necessary through the use of the delay circuit 55 that has been briefly mentioned above.

The output of each of the encoders which is indicated by the Roman numerals I through VIII is fed to the input of a suitable trigger and spark discharge device which have been labelled in block form and have illustrated as their outputs a number of spark discharge devices which simulate spark plugs of an internal combustion engine. It will of course be understood that a number of discharge circuits can be utilized, but for completeness of disclosure there is illustrated in FIG. 3 of the drawings a suitable capacitive discharge circuit that can be utilized with this invention. If the power supply to the capacitive discharge system which is labelled as plus 40() volts is a multi-vibrator type of circuit in a common emitter cor1- figuration with relatively high current transistors, something on the order of 30 amper-es, for example, assume that a trigger is supplied to the trigger input of the SCR 5S, FIG. 3. It will therefore be apparent that the secondary of the converter power supply will be shorted out during the beginning of the spark cycle. This, in effect, causes the multi-vibrator to stop osciliating for a brief span and thus the resonant circuit consisting of the series capacitance 56 and inductance 57 has no high positive voltage to buck and the negative swing of this circuit will turn off the conducting SCR and assure commutation. It will be fairly evident that the diode 53 in series with the power supply to each one of the trigger and spark discharge devices, such as, for example, as shown in FIG. 3, will isolate each circuit so that no improper discharge of capacitors take place on the other cylinders and the converter power supply may be designed so that it need only supply the energy to the capacitor that has just discharged and thus may be of simpler construction than might otherwise be necessitated by a configuration of this nature.

There are, of course, certain design refinements that are not included in the disclosure herein. For example, a conventional trigger isolation circuit should be employed to prevent any damage to the SCR by negative pulses being fed to the gate.

It will of course be apparent that many changes may be made to the circuit from that disclosed herein which more or less would be heralded by technological advances in the field of electronics. For example, instead of conventional light bulbs, technology now permits the utilization of light emitting diodes and with the use of such a device a different light sensor can be utilized particularly one with a stage of gain, such as a light sensitive transistor.

I claim:

1. An electronic ignition system for an internal combustion engine having at least one cylinder including in combination a mechanically driven position encoder, said encoder having one strobe channel for producing a timing output for each cylinder and n position encoding channels wherein 2n is greater than or equal to the number of cylinders, the strobe channel and position encoding channels feeding a logic network, said logic network converting the strobed binary code to a strobed decimal code output, a spark discharge producing means for each cylinder, said strobed decimal coded output triggering said 10 spark discharge producing devices.

2. A system as in claim 1 wherein a delay means is inserted in the strobe channel for providing an advance or retard.

References Cited UNITED STATES PATENTS 2,811,672 10/1957 Gilbert 123-148 2,984,695 5/1961 Berdine et al. 123-148 3,333,183 7/1967 Larrison 250-219 XR LAURENCE M. GOODRIDGE, Primary Examiner.

U.S. Cl. X.R. 315-209; Z50-219 

